Radio station, radio terminal, and synchronization timer control method in radio comunication system

ABSTRACT

A radio station, a radio terminal, and a method for synchronization timer control are provided that can reduce a delay as much as possible until uplink signal resynchronization is done in a case where a plurality of cell groups exist. In a radio communication system having a function of using a plurality of radio resources corresponding to a plurality of cells, respectively, for communication between a radio station (10) and a radio terminal (20), the radio terminal is provided with a plurality of synchronization timers for determining whether or not uplink signals in individual cell groups are in synchronization, wherein the synchronization timers are provided respectively for the plurality of cell groups each including at least one cell, and at the radio terminal (20), uplink-signal transmission on the cells included in a second cell group is controlled depending on a state of a first synchronization timer provided correspondingly for a first cell group including a specific cell and on a state of a second synchronization timer provided correspondingly for the second cell group other than the first cell group, wherein the first synchronization timer and the second synchronization timer are controlled independently.

TECHNICAL FIELD

The present invention relates to a radio communication system in which aradio terminal has a function of transmitting signals on multiplecarriers or multiple cells at the same time and, more particularly, to aradio station, a radio terminal, and a synchronization timer controlmethod in the radio communication system.

BACKGROUND ART

In LTE (Long Term Evolution), which is one of the standards for radiocommunication systems defined by 3GPP (3rd Generation PartnershipProject), radio resources including a time domain and a frequency domainare assigned to each radio terminal (User Equipment: UE) by using theTDM (Time Domain Multiplexing)/FDM (Frequency Domain Multiplexing)scheme. With respect to uplink signals transmitted by multiple radioterminals to a radio base station (enhanced Node B: eNB) in particular,the radio base station controls the transmission timing of an uplinksignal of each radio terminal so that it is accommodated within apredetermined receive window at the radio base station. This control ofuplink-signal transmission timing is performed by using the followingtwo (NPL 1).

-   -   Uplink-signal transmission timing adjustment value (Timing        Advance: TA)    -   Uplink-signal synchronization timer (Time Alignment Timer: TAT)

The transmission timing adjustment value TA is information indicating avalue for a radio terminal to advance or delay the current transmissiontiming by a predetermined amount. The synchronization timer TATindicates a duration for which the timing of receiving an uplink signalat a radio base station is accommodated within a predetermined window,that is, uplink-signal synchronization is guaranteed, with atransmission timing currently configured. The radio terminal is enabledto transmit uplink signals while the synchronization timer TAT isrunning, but does not transmit (is disabled to transmit) uplink signalswhen the synchronization timer TAT expires.

Moreover, in LTE-Advanced (LTE-A), which is a radio communication systemadvanced from LTE, the standardization of carrier aggregation (CA) isbeing proceeded, in which radio terminals use multiple componentcarriers (CC) at the same time to transmit and receive user data and thelike (NPL 2). Each component carrier CC corresponds to one systembandwidth defined in LTE and can be thought to correspond to one cell.That is, a downlink component carrier CC and a corresponding uplinkcomponent carrier CC in combination are thought to be one cell. Forexample, transmission and reception on two downlink (or uplink)component carriers CC can be translated to transmission and reception ontwo cells. Accordingly, communication using a single uplink/downlinkcomponent carrier CC corresponds to communication on a single cell, andin the description hereinafter, both or one of the component carrier andthe cell will be used appropriately.

Here, a component carrier CC that performs the most basic functions suchas obtaining system information required for a radio terminal tocommunicate with a radio base station, is referred to as primarycomponent carrier (Primary CC: PCC) or primary cell (PCell), and othercomponent carriers are referred to as secondary component carrier(Secondary CC: SCC) or secondary cell (SCell).

In LTE-A, studies have hitherto been proceeded on the premise that whencarrier aggregation CA is performed, common uplink-signal transmissiontiming is used on multiple component carriers CC or multiple cells. Thatis, even when uplink signals are transmitted by using multiple componentcarriers (multiple cells corresponding thereto), there is one uplinktransmission timing adjustment value TA that a radio base stationnotifies to a radio terminal at certain time, and there also is onesynchronization timer TAT for each radio terminal. Thereby, it ispossible to easily perform uplink-signal transmission timing controlwithout complicating the control even when carrier aggregation CA isperformed.

On the other hand, in 3GPP, studies of a technology improved from thetechnology standardized as LTE-A have been started. Specifically, thetechnology has been discussed that makes carrier aggregation CA feasibleeven if uplink-signal transmission timing differs between a plurality ofcomponent carriers CC, that is, a plurality of cells. Factors causinguplink-signal transmission timing to differ between a plurality ofcomponent carriers CC (a plurality of cells) are different frequencybands, a repeater (repeating station) being set for each frequency band(or only for a specific frequency band), and the like.

In 3GPP, a group of one or a plurality of component carriers (cells) onwhich uplink-signal transmission timing can be controlled in common isreferred to as synchronization group (Timing Advance Group: TA Group).NPL 3 proposes a method for controlling synchronization timers, in whichthe uplink-signal transmission timing adjustment value TA is controlledfor each such TA Group on which timing control can be performed incommon, and in which one synchronization timer TAT is maintained alsofor each TA Group.

Hereinafter, a brief description will be given of a method forcontrolling synchronization timers in a case where uplink-signaltransmission timing differs between a plurality of component carriers CC(a plurality of cells), with reference to FIGS. 1 to 3.

Referring to FIG. 1, a system will be considered in which two TA Groups1 and 2 with different uplink-signal transmission timings exist. Here,it is assumed that a primary cell PCell and a secondary cell SCell1belong to the same TA Group 1, and secondary cells SCell2 and SCell3belong to the same TA Group 2 as shown in FIG. 2A, and that to a radiobase station eNB, a radio terminal UE performs uplink transmission byusing the three secondary cells SCell1-3 in addition to the primary cellPCell. In this case, since uplink transmission timing differs betweenthe TA Groups 1 and 2, uplink transmission timing adjustment values TA1and TA2 for the respective TA Groups are configured so that uplinksignal reception timing at the radio base station eNB will beaccommodated within a predetermined window as shown in FIG. 2B.

Moreover, referring to FIG. 3, according to NPL 3, a radio terminal UEcontrols a synchronization timer TAT1, linking it with uplink-signaltransmission timing control on the TA Group 1, and similarly controls asynchronization timer TAT2, linking it with uplink-signal transmissiontiming control on the TA Group 2. That is, when uplink-signalsynchronization is established in the individual TA Groups (TA Groups 1and 2), the respective corresponding synchronization timers TAT1 andTAT2 are started, and each time transmission timing adjustment valuesTA1 and TA2 are received while the synchronization timers TAT1 and TAT2are running for the respective TA Groups, the synchronization timersTAT1 and TAT2 are restarted (restarted from a set value) (Steps S11 andS12). According to this timer control, the radio terminal UE candetermine whether or not uplink-signal synchronization in each TA Groupis guaranteed.

Moreover, it is proposed that when the synchronization timer TAT1 forthe TA Group 1 expires (Step S13), the synchronization timer TAT2 isstopped (Step S14) even if the synchronization timer TAT2 is running atthat time, that is, even if uplink signals in the TA Group 2 are insynchronization. This proposal is based on the restriction according toCA in LTE-A that a radio terminal UE can transmit uplink control signals(Physical Uplink Control Channel: PUCCH) only on the primary cell. Thatis, when an uplink signal on the primary cell, on which uplink controlsignals (PUCCH) can be transmitted, is not in synchronization, a radioterminal UE should stop transmission of all uplink signals, and theproposal aims to easily implement this by configuring thesynchronization timer TAT2 to be stopped upon expiry of thesynchronization timer TAT1.

Note that after the synchronization timer TAT2 is stopped, the radioterminal UE does not restart the synchronization timer TAT2 even when atransmission timing adjustment value TA2 for the TA Group 2 is received.Thereby, it is possible to avoid a situation where the radio terminal UEtransmits an uplink signal in the TA Group 2 when the synchronizationtimer TAT1 expires but the synchronization timer TAT2 is running.

CITATION LIST Patent Literature [NPL 1]

3GPP TS 36.321 v10.1.0 (the Internet<URL>http:www.3gpp.org/ftp/Specs/html-info/36321.htm), Section 5.2

[NPL 2]

3GPP TS 36.300 v10.3.0 (the Internet<URL>http:www.3gpp.org/ftp/Specs/html-info/36300.htm), Sections 5.5,6.4, and 7.5

[NPL 3]

3GPP RAN WG2 Contribution, R2-112819 (the Internet<URL>http:www.3gpp.org/ftp/tsg_ran/WG2_RL2/TSGR2_74/Docs/R2-112819.zip)

SUMMARY OF INVENTION Technical Problem

According to the above-described synchronization timer control in LTE,when the synchronization timer TAT1 for the TA Group 1 including theprimary cell expires, the synchronization timer TAT 2 for the TA Group 2is stopped. However, the carrier aggregation (CA) that is currentlyconsidered in 3GPP premises that processing for establishingsynchronization cannot be performed in parallel in a plurality of TAGroups. Therefore, if uplink signal resynchronization is required atleast on a cell of the TA Group 1 including the primary cell and furtheruplink signal resynchronization is also required on a cell of the TAGroup 2, resynchronization in the TA Group 1 is first completed, andthereafter resynchronization in the TA Group 2 is started. Accordingly,resynchronization operation in the TA Group 2 is started after as long adelay as the time required for resynchronization in the TA Group 1. Thetime required for resynchronization in a TA Group is assumed to be about20 msec (or more). Since this delay time increases proportionately withthe number of TA Groups and greatly lowers the transmission rate(throughput) of a radio terminal, it is preferable to make this delaytime as short as possible. Note that an assumable case whereresynchronization is required in both the TA Groups 1 and 2 is that, forexample, carrier aggregation (CA) is required (CA is preferred) becausea radio terminal UE is executing an application or the like thatperforms data transmission on a one-shot basis and data to betransmitted at a time has a large size.

As described above, in order to avoid a decrease in the throughput of aradio terminal, it is important to avoid a delay in the completion ofresynchronization in another TA Group occurring when the synchronizationtimer TAT1 for the TA Group 1 including the primary cell expires andsynchronization is lost.

Accordingly, an object of the present invention is to provide a radiostation, a radio terminal, and a synchronization timer control method ina radio communication system, which reduce a delay in uplink signalresynchronization as much as possible in a case where a plurality ofcell groups exist.

Solution to Problem

A radio terminal according to the present invention is a radio terminalhaving a function of communicating with a radio station by using aplurality of radio resources that correspond respectively to a pluralityof cells, characterized by comprising: a plurality of synchronizationtimers for determining whether or not uplink signals in individual cellgroups are in synchronization, wherein the synchronization timers areprovided respectively for the plurality of cell groups each including atleast one cell; and control means that controls uplink-signaltransmission on the cells included in a second cell group depending on astate of a first synchronization timer provided correspondingly for afirst cell group including a specific cell and on a state of a secondsynchronization timer provided correspondingly for the second cell groupother than the first cell group, and controls the first synchronizationtimer and the second synchronization timer independently.

A method for synchronization timer control at a radio terminal accordingto the present invention is a method for synchronization timer controlat a radio terminal that has a function of communicating with a radiostation by using a plurality of radio resources correspondingrespectively to a plurality of cells and includes a plurality ofsynchronization timers for determining whether or not uplink signals inindividual cell groups are in synchronization, wherein thesynchronization timers are provided respectively for the plurality ofcell groups each including at least one cell, characterized bycomprising: controlling uplink-signal transmission on the cells includedin a second cell group depending on a state of a first synchronizationtimer provided correspondingly for a first cell group including aspecific cell and on a state of a second synchronization timer providedcorrespondingly for the second cell group other than the first cellgroup; and controlling the first synchronization timer and the secondsynchronization timer independently.

A radio station according to the present invention is a radio stationhaving a function of communicating with a radio terminal by using aplurality of radio resources that correspond respectively to a pluralityof cells, characterized by comprising: a plurality of synchronizationtimers for determining whether or not uplink signals in individual cellgroups are in synchronization, wherein the synchronization timers areprovided respectively for the plurality of cell groups each including atleast one cell; and control means that controls scheduling ofuplink-signal transmission of the radio terminal on the cells includedin a second cell group, depending on a state of a first synchronizationtimer provided correspondingly for a first cell group including aspecific cell and on a state of a second synchronization timer providedcorrespondingly for the second cell group other than the first cellgroup, and controls the first synchronization timer and the secondsynchronization timer independently.

A method for synchronization timer control at a radio station accordingto the present invention is a method for synchronization timer controlat a radio station that has a function of communicating with a radioterminal by using a plurality of radio resources correspondingrespectively to a plurality of cells and includes a plurality ofsynchronization timers for determining whether or not uplink signals inindividual cell groups are in synchronization, wherein thesynchronization timers are provided respectively for the plurality ofcell groups each including at least one cell, characterized bycomprising: controlling scheduling of uplink-signal transmission on thecells included in a second cell group, depending on a state of a firstsynchronization timer provided correspondingly for a first cell groupincluding a specific cell and on a state of a second synchronizationtimer provided correspondingly for the second cell group other than thefirst cell group; and controlling the first synchronization timer andthe second synchronization timer independently.

A radio communication system according to the present invention is aradio communication system having a function of using a plurality ofradio resources corresponding respectively to a plurality of cells, forcommunication between a radio station and a radio terminal,characterized in that the radio terminal is provided with a plurality ofsynchronization timers for determining whether or not uplink signals inindividual cell groups are in synchronization, wherein thesynchronization timers are provided respectively for the plurality ofcell groups each including at least one cell, and at the radio terminal,uplink-signal transmission on the cells included in a second cell groupis controlled depending on a state of a first synchronization timerprovided correspondingly for a first cell group including a specificcell and on a state of a second synchronization timer providedcorrespondingly for the second cell group other than the first cellgroup, wherein the first synchronization timer and the secondsynchronization timer are controlled independently.

Advantageous Effects of Invention

According to the present invention, uplink-signal transmission in asecond cell group is controlled depending on the state of a firstsynchronization timer and the state of a second synchronization timer,and the first and second synchronization timers are controlledindependently of each other, whereby it is possible to allow the secondsynchronization timer to continue running when the first synchronizationtimer expires, and it is possible to reduce a delay until the completionof resynchronization in the second cell group in a case whereresynchronization in the first cell group is performed. Thus, it ispossible to suppress a decrease in the throughput of a radio terminaldue to such a delay.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a system for describing synchronizationgroups in LTE-Advanced.

FIG. 2A is a schematic diagram for describing carrier aggregation in thesystem shown in FIG. 1, and FIG. 2B is a schematic diagram fordescribing uplink-signal transmission timing adjustment values for thesynchronization groups shown in FIG. 2A.

FIG. 3 is a sequence diagram showing operations of a radio terminal anda radio base station in synchronization timer control shown in FIG. 2.

FIG. 4 is a schematic diagram showing an example of cell groups fordescribing carrier aggregation in a radio communication system accordingto an exemplary embodiment of the present invention.

FIG. 5 is a schematic diagram showing another example of cell groups fordescribing carrier aggregation in the radio communication systemaccording to the present exemplary embodiment.

FIG. 6 is a sequence diagram showing operations of a radio terminal anda radio base station in the radio communication system according to thepresent exemplary embodiment.

FIG. 7 is a block diagram showing a functional configuration of theradio base station according to the present exemplary embodiment.

FIG. 8 is a block diagram showing a functional configuration of theradio terminal according to the present exemplary embodiment.

FIG. 9 is a flowchart showing a method for synchronization timer controlat the radio base station according to a first example of the presentinvention.

FIG. 10 is a flowchart showing a method for synchronization timercontrol at the radio terminal according to the first example of thepresent invention.

FIG. 11 is a flowchart showing a method for synchronization timercontrol at the radio base station according to a second example of thepresent invention.

FIG. 12 is a flowchart showing a method for synchronization timercontrol at the radio terminal according to the second example of thepresent invention.

FIG. 13 is a schematic diagram showing an example of synchronizationgroups for describing carrier aggregation in a radio communicationsystem that is a concrete application example of the present exemplaryembodiment.

FIG. 14 is a flowchart showing a method for synchronization timercontrol at a radio base station according to a third example of thepresent invention.

FIG. 15 is a flowchart showing a method for synchronization timercontrol at a radio terminal according to the third example of thepresent invention.

FIG. 16 is a flowchart showing a method for synchronization timercontrol at the radio terminal according to a fourth example of thepresent invention.

DESCRIPTION OF EMBODIMENTS

According to the present invention, a plurality of synchronizationtimers for determining whether or not uplink signals of a radio terminalare in synchronization are maintained correspondingly to a plurality ofrespective cell groups each including at least one cell. Uplink-signaltransmission on a cell included in the second cell group is controlleddepending on the state of a first synchronization timer corresponding toa first cell group, which includes a specific cell among the pluralityof cell group, and on the state of a second synchronization timercorresponding to a second cell group other than the first cell group,and the first and second synchronization timers are controlledindependently of each other. Here, it can be thought that a cell groupconsists of cells on which the same uplink-signal transmission timingcan be used.

According to such control, when the first synchronization timer for thefirst cell group including the specific cell expires, it is possible toallow the second synchronization timer for the second cell group, whichis another cell group, to independently continue running. Accordingly,by stopping at least uplink-data transmission on the cells of the secondcell group while having the second synchronization timer for the secondcell group continue running, uplink-signal transmission on the cells ofthe second cell group can be immediately performed without delay whenresynchronization is established on a cell (for example, the specificcell) included in the first cell group and the first synchronizationtimer for the first cell group is started. Hereinafter, an exemplaryembodiment and some examples of the present invention will be describedin detail.

1. Exemplary Embodiment 1.1) System Architecture

In an exemplary embodiment of the present invention, a radiocommunication system including a radio station and a radio terminal isassumed, and for the radio station, a radio base station, a base stationcontroller, or the like can be assumed. In the present exemplaryembodiment and examples, which will be described later, a descriptionwill be given assuming that the radio station is a radio base station asan example.

FIG. 4 shows only one sector in order to avoid complicating the drawing,but an ordinary configuration includes a plurality of sectors. A radiobase station 10 manages cells 0 to 3 using four frequency bands f0, f1,f2, and f3, and a radio terminal 20 can transmit uplink signals by usinga plurality of frequency bands at the same time. That is, the radioterminal 20 can transmit uplink signals by using, at the same time, allor some of an uplink radio resource on the cell 0 of the frequency bandf0 (hereinafter, simply referred to as cell 0), an uplink radio resourceon the cell 1 of f1 (hereinafter, simply referred to as cell 1), anuplink radio resource on the cell 2 of f2 (hereinafter, simply referredto as cell 2), and an uplink radio resource on the cell 3 of f3(hereinafter, simply referred to as cell 3), wherein the radio resourcesmeet a predetermined condition. The predetermined condition here isthat, for example, in accordance with uplink radio resourceconfiguration information received from the radio base station 10, thisradio resource is (explicitly or inexplicitly) activated and is in anavailable state.

Moreover, these plurality of cells 0 to 3 (that is, the respectiveuplink radio resources) are grouped in accordance with a predeterminedrule, and here it is assumed that the cells 0 and 1 are grouped into acell group 1 and the cells 2 and 3 are grouped into a cell group 2. Thepredetermined rule here is that, for example, propagation delays(propagation characteristics) are identical (similar) and so the sameuplink-signal transmission timing adjustment value can be applied (used)(transmission timing configuration can be shared). Uplink-signaltransmission timing control of the radio terminal 20 is performed inunits of such a cell group.

Further, the radio base station 10 and the radio terminal 20 havesynchronization timers used to determine whether or not uplink signalsare in synchronization, which are provided for cell groups respectivelyand are controlled (started, restarted, or stopped) independently ofeach cell group. Specifically, of the synchronization timers provided tothe radio base station 10/radio terminal 20, a synchronization timer 1is started or restarted each time a “transmission timing adjustmentvalue” for adjusting uplink-signal transmission timing on the cells ofthe cell group 1 is transmitted/received, while a synchronization timer2 is started or restarted each time a transmission timing adjustmentvalue for the cells of the cell group 2 is transmitted/received. Notethat a “cell group” here does not necessarily include a plurality ofcells as shown in FIG. 4, but some cell group may include only one cell.

Hereinafter, synchronization timer control according to the presentexemplary embodiment will be described by taking, as an example, asystem in which a cell group 1 (specific group) includes only a specificcell 1 and a cell group 2 (non-specific group) includes only anon-specific cell 2 as shown in FIG. 5, for simplicity. The specificcell 1 has roles different from the non-specific cell 2. For example,the specific cell 1 is used to perform processing for establishing aninitial radio connection required for the radio terminal 20 tocommunicate with the radio base station 10, as well as to obtain basicinformation such as security information and to transmit controlsignals. However, it is obvious from a description below that thepresent invention can similarly be applied to a system in which a cellgroup includes a plurality of cells. Moreover, although shown in FIG. 5is a 3-sector configuration (three sector cells per radio base station),the present invention is not limited to this but can similarly beapplied to configurations other than the 3-sector one such as, forexample, 1-sector and 6-sector ones. Further, conceivable cases whereuplink-signal transmission timings on the cells 1 and 2 need to beindependently controlled are cases where f1 and f2 are greatly different(for example, 800 MHz and 2 GHz), where a reproduction station (arepeater) exists for each or one of f1 and f2, and the like.

1.2) Synchronization Timer Control

Referring to FIG. 6, the synchronization timers 1 and 2 are provided tothe radio terminal 20 correspondingly for the cell group 1 (specificgroup) and the cell group 2 (non-specific group), respectively, and arecontrolled independently for each cell group. Note that it isconceivable that synchronization timers (not shown) corresponding to thesynchronization timers 1 and 2 are similarly provided to the radio basestation 20. That is, the synchronization timers 1 and 2 are started whenuplink-signal synchronization is established on the cells of theirrespective cell groups; while they are running, the radio base station10 transmits transmission timing adjustment values TA1 and TA2; when theradio terminal 20 receives them, the corresponding synchronizationtimers1 and 2 are restarted (Steps S21 and S22). According to such timercontrol, depending on whether or not the synchronization timers 1 and 2are running, the radio terminal UE can determine whether or notuplink-signal synchronization is guaranteed in the respective cellgroups.

According to the present exemplary embodiment, the state of thesynchronization timer 1 for the cell group 1 (specific group) isassociated not only with uplink-signal (for example, uplink-data)transmission on the cell 1 included in the cell group1 but also withuplink-signal transmission on the cell 2 included in the cell group 2(non-specific group) other than the cell group 1. “Associate” here meansthat the state of a synchronization timer for a certain cell group isalso linked with enabling/disabling uplink-signal transmission on thecells of another cell group, not only of this certain cell group. Forexample, when the synchronization timer 1 for the cell group 1 expires,not only transmission of uplink signals (except access signals that canbe transmitted when synchronization is lost) on the cell 1 included inthis cell group 1 is stopped, but transmission of some or all uplinksignals on the cell 2 included in the cell group 2 is also stopped.Here, a conceivable case where transmission of some uplink signals isstopped (is not performed) is, but is not limited to, a case wheretransmission of data is stopped but transmission of control signalsand/or known signals (pilot signals and reference signals) is notstopped, that is, continues to be performed. “Associate” illustrated inFIG. 6 is as follows.

Referring to FIG. 6, when the synchronization timer 1 for the cell group1 (specific group) expires (Step S23), uplink transmission on the cell 1included in the cell group 1 falls in an out-of-synchronization state(is regarded to be in an out-of-synchronization state) and is stopped.If the synchronization timer 2 for the cell group 2 (non-specific group)is running at this time, this synchronization timer 2 is not stopped butis left continuously running (Step S24), while at least uplink datatransmission on the cell 2 included in the non-specific group 2 isstopped (Step S25). However, an uplink access signal forsynchronization/resynchronization (for example, a random accesspreamble) can be transmitted as necessary. The radio base station 10,when the synchronization timer 1 expires, stops uplink-signal schedulingon the cell 1 included in the cell group 1.

The radio base station 10 and the radio terminal 20 perform processingfor resynchronization on the cell 1 included in the cell group 1 if anuplink signal needs to be transmitted again in the cell groups 1 and 2(Step S26). When resynchronization is established, the synchronizationtimer 1 for the cell group 1 is started, allowing uplink transmission onthe cell 1 included in the cell group 1 to be in an in-synchronizationstate. If the synchronization timer 2 for the cell group 2 is running(is not expired) at this time, uplink transmission is restarted on thecell 2 included in the cell group 2, enabling uplink transmissionincluding uplink data transmission (Step S27). Here, enablinguplink-signal transmission means that when a radio resource foruplink-signal transmission is scheduled (assigned), transmission can beperformed in accordance with such scheduling. Note that if radioresources for periodic transmission of an uplink signal have alreadybeen scheduled (assigned), the meaning is that transmission can beperformed by using such scheduled radio resources.

1.3) Effects

As described above, according to the present exemplary embodiment, evenwhen the synchronization timer 1 for the cell group 1 (specific group)expires, the synchronization timer 2 for the cell group 2 (non-specificgroup), if it is running, is left continuously running, while at leastuplink data transmission on the cell of the cell group 2 is stopped.Then, when resynchronization in the cell group 1 is established and thesynchronization timer 1 for the cell group 1 is started, uplinktransmission on the cell of the cell group 2 can immediately beperformed if the synchronization timer 2 for the cell group 2 is stillrunning.

In this manner, enabling/disabling uplink-signal transmission in thecell group 2 is linked with the state of the synchronization timer 1 forthe cell group 1, whereby as long as the synchronization timer 2 isrunning, uplink-signal transmission on the cell of the cell group 2 canbe restarted immediately (for example, when uplink schedulinginformation is received, without awaiting resynchronization), and so itis possible to reduce a delay occurring when resynchronization isperformed, and to suppress a decrease in the throughput of the radioterminal.

2. Functional Configurations of Radio Station and Radio Terminal

Referring to FIG. 7, the radio base station 10 as a radio station have areception section 101 that receives signals from a plurality of radioterminals individually and a demodulation section 102 that demodulatesthe received signals, and received user data is processed at an upperlayer 103. A timing control unit 104 is provided correspondingly foreach of the plurality of radio terminals and transmits theabove-described respective uplink-signal transmission timing adjustmentvalues for cell groups that are used by each radio terminal, thuscontrolling the transmission timings of uplink signals to be transmittedby the corresponding radio terminal. A transmission signal generationsection (Tx signal generator) 105 generates downlink signals to theradio terminals, and a transmission section 106 transmits the downlinksignals.

The timing control unit 104 includes, as functional components, thesynchronization timer 1 (at reference sign 107 p in FIG. 7) used todetermine whether or not uplink signals in the cell group 1 (specificgroup) at a radio terminal x are in synchronization, the synchronizationtimer 2 (at reference sign 107 s in FIG. 7) used to determine whether ornot uplink signals in the cell group 2 (non-specific group) at the radioterminal x are in synchronization, a TA1 calculation and retentionsection 108 that calculates and retains a transmission timing adjustmentvalue TA1 for the cell of the cell group 1, and a TA2 calculation andretention section 109 that calculates and retains a transmission timingadjustment value TA2 for the cell of the cell group 2.

Note that here illustrated is a case of two synchronization groups asshown in FIG. 5, that is, the cell group 1 (specific group) and the cellgroup 2 (non-specific group), but if there are three or more cell groups(one specific group and two or more non-specific groups), asynchronization timer and an uplink-signal transmission timingadjustment value calculation and retention section are provided for eachof them.

Referring to FIG. 8, the radio terminal 20 includes a reception section201 that receives signals from the radio base station 10, a demodulationsection 202 that demodulates the received downlink signals, an upperlayer 203 that processes downlink data, a timing control unit 204 thatperforms control of uplink-signal transmission timing in each cell groupin accordance with an uplink-signal transmission timing adjustment valuefrom the radio base station 10, a transmission signal generation section205 that generates uplink signals to the radio base station 10, and atransmission section 206 that transmits the uplink signals.

The timing control unit 204 includes, as functional components, a TA1management unit 208 that controls transmission timing on the cell of thecell group 1 in according with an uplink-signal transmission timingadjustment value TA1 from the radio base station 10 and a TA2 managementunit 209 that controls transmission timing on the cell of the cell group2 in according with an uplink-signal transmission timing adjustmentvalue TA2 from the radio base station 10. Further, the TA1 managementunit 208 includes the synchronization timer 1 (at reference sign 210 pin FIG. 8) used to determine whether or not uplink-signal transmissiontiming in the cell group 1 is in synchronization, and the TA2 managementunit 209 includes the synchronization timer 2 (at reference sign 210 sin FIG. 8) used to determine whether or not uplink-signal transmissiontiming in the cell group 2 is in synchronization.

Note that the functions of the timing control unit 104 in the radio basestation 10 shown in FIG. 7 can also be implemented by executing programsstored in a memory (not shown) on a program-controlled processor such asa CPU. Similarly, the functions of the timing control unit 204 in theradio terminal 20 shown in FIG. 8 can also be implemented by executingprograms stored in a memory (not shown) on a program-controlledprocessor such as a CPU.

Hereinafter, basic operations for synchronization timer control of theradio base station 10 and the radio terminal 20 shown in FIGS. 7 and 8will be described in detail with reference to FIGS. 9 and 10.

3. First Example 3.1) Synchronization Timer Control

FIGS. 9 and 10 show basic operations of the radio base station 10 andthe radio terminal 20 according to a present example, respectively.Here, at a stage preliminary to data transmission, the radio terminal 20makes a scheduling request (Scheduling Request: SR) to request an uplinkradio resource and a transmission buffer status report (Buffer StatusReport: BSR) as necessary. However, steps concerning such a schedulingrequest are omitted in FIGS. 9 and 10.

Referring to FIG. 9, the timing control unit 104 of the radio basestation 10 first determines whether or not there is uplink transmissiondata that a target radio terminal x requests to transmit (Step 301) and,when there is uplink transmission data (Step 301: Yes), determineswhether or not the synchronization timer 1 (107 p) for the cell group 1is running (Step 302).

When the synchronization timer 1 (107 p) is not running (expires) (Step302; No), the timing control unit 104 gives instructions for uplinkresynchronization on the cell 1 (Step 303). When resynchronization iscompleted on the cell 1 (Step 304; Yes), it is determined whether or notthe synchronization timer 2 (107 s) for the cell group 2 is running(Step 305).

When the synchronization timer 2 (107 s) is running (Step 305; Yes), thetiming control unit 104 performs uplink scheduling on the cell 1 and/orcell 2 for the radio terminal x (Step 306) and notifies a schedulinggrant (a result of scheduling) (Step 307).

When the synchronization timer 2 (107 s) is not running (expires) (Step305; No), the timing control unit 104 determines whether or notresynchronization on the cell 2 is required (Step 308) and, when it isrequired (Step 308; Yes), gives instructions for uplinkresynchronization on the cell 2 (Step 309). Step 309 is not performed ifresynchronization on the cell 2 is not required (Step 308; No). Then,the timing control unit 104 performs uplink scheduling on the cell 1 forthe radio terminal x (Step 310) and notifies a scheduling grant (Step307). Note that the radio base station 10 can also perform uplinkscheduling on the cell 2 when uplink resynchronization on the cell 2 isconfirmed.

Referring to FIG. 10, the timing control unit 204 of the radio terminal20, after making a scheduling request and a transmission buffer statusreport (not shown), determines whether or not an uplink scheduling grantis received (Step 401) and, when it is received (Step 401; Yes),transmits uplink data on the cell 1 and/or cell 2 in accordance withthis scheduling grant (Step 402).

When no uplink scheduling grant is received (Step 401; No), the timingcontrol unit 204 determines whether or not the synchronization timer 1(210 p) for the cell group 1 is running (Step 403) and, when it isrunning (Step 403; Yes), similarly performs determination as to thesynchronization timer 2 (210 s) for the cell group 2 (Step 404). Whenthe synchronization timer 2 (210 s) is not running (Step 404; No), it isdetermined whether or not a trigger for uplink resynchronization on thecell 2 is issued (Step 405). Here, conceivable triggers forresynchronization include, for example, instructions forresynchronization from the radio base station 10, a result ofdetermination made by the radio terminal itself, concluding that theamount of data in an uplink transmission buffer reaches or exceeds apredetermined value and transmission using a plurality of cells ispreferable, or alternatively the fact that uplink synchronization ismaintained on another cell (in another cell group) to be simultaneouslyused, and the like.

When a trigger for uplink resynchronization on the cell 2 is issued(Step 405; Yes), processing required for uplink resynchronization on thecell 2 is performed (Step 406). For example, conceivable processing forresynchronization is processing in which an access signal for randomaccess or the like is transmitted and an uplink-signal transmissiontiming adjustment value is obtained, or the like. When resynchronizationon the cell 2 is completed (Step 407; Yes), the synchronization timer 2(210 s) is started (Step 408), and the series of steps is finished. Whenthe synchronization timer 2 (210 s) is running (Step 404; Yes), or whenno trigger for uplink resynchronization on the cell 2 is issued (Step405; No), the series of steps is immediately finished.

Moreover, when the synchronization timer 1 (210 p) is not running (Step403; No), it is determined whether or not a trigger for uplinkresynchronization on the cell 1 is issued (Step 409). When a trigger isissued (Step 409; Yes), processing required for uplink resynchronizationon the cell 1 is performed (Step 410), and when resynchronization iscompleted (Step 311; Yes), the synchronization timer 1 (210 p) isstarted (Step 412), and the series of steps is finished.

Further, when no trigger for uplink resynchronization on the cell 1 isissued (Step 409; No), it is determined whether or not thesynchronization timer 2 (210 s) for the cell group 2 is running (Step413). When it is running (Step 413; Yes), uplink data transmission onthe cell 2 is stopped (is not performed) until resynchronization on thecell 1 is completed (Step 414). At this time, the synchronization timer2 (210 s) is left continuously running (Step 415), and the series ofsteps is finished. Note that in this case, although uplink datatransmission is stopped on the cell 2, known signals such as controlsignals and reference signals may be transmitted. If the synchronizationtimer 2 (210 s) is not running (Step 413; No), the series of steps isimmediately finished.

Note that in a case where a cell group includes a plurality of cells asshown in FIG. 4, the radio base station 10 calculates an uplink-signaltransmission timing adjustment value for each cell group and notifies itto the radio terminal 20. In this event, an uplink signal on any ofcells may be used to calculate an uplink-signal transmission timingadjustment value as long as the cells are of a cell group. When theradio terminal 20 receives a transmission timing adjustment value, theradio terminal 20, for each cell group, applies the receivedtransmission timing adjustment value to all the cells included in thecell group. According to such control, in a case where the radioterminal 20 uses uplink radio resources on respective cells of aplurality of cell groups in each of which uplink-signal transmissiontiming control needs to be performed independently, it is possible toappropriately perform uplink-signal synchronization management by usingsynchronization timers that operate independently for the respectivecell groups.

3.2) Effects

According to the above-described synchronization timer control, evenwhen the synchronization timer 1(210 p) for the cell group 1 (specificgroup) expires, the synchronization timer 2 (210 s) for the cell group 2(non-specific group) is left continuously running if it is running,while at least uplink data transmission on the cell of the cell group 2is stopped. Then, when resynchronization in the cell group 1 isestablished and the synchronization timer 1 (210 p) for the cell group 1is started, uplink transmission on the cell of the cell group 2 can beperformed without performing resynchronization processing if thesynchronization timer 2 (210 s) for the cell group 2 is still running.

4. Second Example

In synchronization timer control according to a second example of thepresent invention shown in FIG. 11, attention is given to processingconcerning a scheduling request, data transmission, and the likeperformed by the radio terminal 20 after the synchronization timer 1 forthe cell group 1 expires.

4.1) Synchronization Timer Control

Referring to FIG. 11, at the radio base station 10, when thesynchronization timer 1 for the cell group 1 expires (Step 501), it isdetermined whether or not the synchronization timer 2 for the cell group2 is running (Step 502). When the synchronization timer 2 is running(Step 502; Yes), uplink scheduling on the cell 2 (even though it isrequired) is stopped (Step 503), while the synchronization timer 2 isleft continuously running (Step 504). If the synchronization timer 2 isnot running (Step 502; No), steps 503 and 504 are not performed.

Subsequently, it is determined whether or not uplink resynchronizationis done on the cell 1 (Step 505), and when resynchronization is done(Step 505; Yes), the synchronization timer 1 is started (Step 506).Here, a conceivable reason for establishing uplink resynchronization onthe cell 1 is to cause the radio terminal 20 to transmit uplink data, tocause the radio terminal 20 to transmit a response (control signal) todownlink data transmission made to the radio terminal 20, or the like.

Subsequently, it is determined whether or not the synchronization timer2 is running (Step 507), and if it is still running (Step 507; Yes), itis determined whether or not an uplink extended scheduling request isreceived (Step 508). Here, the extended scheduling request is a requestthat is used when uplink signals are transmitted using (uplink radioresources on) a plurality of cells and that can request (for example)more resources than a conventional scheduling request. If an extendedscheduling request is received (Step 508; Yes), scheduling grants on thecells 1 and 2 are notified to the radio terminal 20 (Step 509).

Moreover, when the synchronization timer 2 is not running (Step 507;No), or when no extended scheduling request is received (Step 508; No),it is determined whether or not an ordinary scheduling request isreceived (Step 510). If a conventional scheduling request is received(Step 510; Yes), a scheduling grant on the cell 1 is notified to theradio terminal 20 (Step 511).

Referring to FIG. 12, at the radio terminal 20, when the synchronizationtimer 1 for the cell group 1 expires (Step 601), it is determinedwhether or not the synchronization timer 2 for the cell group 2 isrunning (Step 602). When the synchronization timer 2 is running (Step602; Yes), uplink data transmission on the cell 2 (even if it isscheduled) is stopped (is not performed) (Step 603), while thesynchronization timer 2 is left continuously running (Step 604). Then,processing for resynchronization on the cell 1 is performed as necessary(not shown).

When resynchronization on the cell 1 is done (Step 605; Yes), thesynchronization timer 1 is started (Step 606), and it is determinedwhether or not there is uplink data to transmit (Step 607). When thereis uplink data (Step 607; Yes), it is determined whether or not thesynchronization timer 2 is still running (Step 608).

When the synchronization timer 2 is running (Step 608; Yes), an extendedscheduling request is transmitted (Step 609). When uplink schedulinggrants on the cells 1 and 2 are received as a response to the extendedscheduling request (Step 610), uplink data is transmitted on each of thecells 1 and 2 in accordance with the grants (Step 611). If thesynchronization timer 2 is not running (Step 608; No), an ordinaryscheduling request is transmitted (Step 612). When an uplink schedulinggrant on the cell 1 is received as a response to the scheduling request(Step 613), uplink data is transmitted on the cell 1 in accordance withthe grant (Step 614).

4.2) Effects

According to the above-described synchronization timer control of thepresent example, when uplink synchronization is reestablished on thecell 1 after the synchronization timer 1 for the cell group 1 includingthe cell 1 is once expired, uplink data transmission can also beperformed on the cell 2 immediately without need to reestablish uplinksynchronization in the cell group 2 including the cell 2. That is, it ispossible to suppress a delay until uplink data transmission is performedagain using (uplink radio resources on) a plurality of cells. Note thateven if the radio terminal 20 transmits an extended scheduling request,scheduling grants on both the cells 1 and 2 are not necessarilyreceived, but a scheduling grant may be on any one of them. Moreover,even if the synchronization timer 2 is running, an ordinary schedulingrequest may be made. It is needless to say that such cases are alsoincorporated in the scope of application of the present invention.Further, it is also obvious that the present invention can also beapplied in cases where there are three or more cell groups in each ofwhich uplink-signal transmission timing control is performedindependently.

5. Application Example

As a concrete application example of the present invention, a radiocommunication system in conformity with 3GPP LTE (Long Term Evolution)will be described in detail. As described already, in LTE, carrieraggregation (CA) is defined in which a radio terminal (User Equipment:UE) transmits and receives user data and upper layer control informationby simultaneously using a plurality of component carriers (CC) thatcorrespond to a plurality of cells respectively. The present inventioncan be applied to such carrier aggregation CA in LTE.

In the functionality of the carrier aggregation CA, a cell used by aradio terminal UE to obtain system information and security informationthat are most fundamental in communication with a radio base station eNBis referred to as primary cell (PCell), and other cells which are usedsimultaneously with the primary cell PCell are referred to as secondarycell (SCell). That is, the radio terminal UE can transmit and receiveuser data and the like by using the single primary cell PCell and one ormore secondary cells SCell at the same time.

Note that in preparation for performing downlink carrier aggregation CA,the radio base station eNB first configures secondary cells SCell(configure SCell) for the radio terminal UE. In this event, minimumcomponents required to configure secondary cells are information aboutcomponent carriers CC corresponding to downlink radio resources. Then, asecondary cell to be actually used is selected among the configuredsecondary cells (configured SCell), and instructions are made to theradio terminal UE to activate this secondary cell (activation of SCell).Thereafter, the radio terminal UE can receive downlink signals by usingthe actually activated secondary cell (activated SCell) and the primarycell PCell at the same time.

On the other hand, in preparation for performing uplink carrieraggregation CA, the radio base station eNB notifies, in addition toinformation about a downlink component carrier CC, information about acomponent carrier CC corresponding to a relevant uplink radio resourcewhen a secondary cell is configured for the radio terminal UE. Then,after this secondary cell is activated (activation of SCell withconfigured uplink), the uplink component carrier CC (uplink radioresource) of this secondary cell SCell can be used.

Here, a set of cells that respectively correspond to a plurality ofuplink radio resources (component carriers CC) to which the sametransmission timing adjustment value (Timing Advance: TA) can be applied(used or shared) is referred to as synchronization group (Timing AdvanceGroup: TA Group). The synchronization group (TA Group) corresponds tothe above-described cell group. However, each synchronization group (TAGroup) includes one or more cells. That is, each synchronization group(TA Group) may be configured with only one cell. Moreover, asynchronization group (TA Group) that includes the primary cell PCell isreferred to as primary synchronization group (Primary TA Group or PCellTA Group), and a synchronization group (TA Group) that includes onlysecondary cells SCell is referred to as secondary synchronization group(Secondary TA Group or SCell TA Group). The primary synchronizationgroup consists of only the primary cell PCell or consists of the primarycell PCell and one or more secondary cells SCell, and the secondarysynchronization group consists of one or more secondary cells SCell.Note that in LTE, information indicating a transmission timingadjustment value (TA) is referred to as TA command (Timing AdvanceCommand), which is transmitted as control information (Control Element:CE) on the MAC Layer (Medium Access Control Layer).

In a case where the present invention is provided to such a system, asynchronization timer (Time Alignment Timer: TAT) used to determinewhether or not uplink signals of a radio terminal UE are insynchronization is maintained for each synchronization group. Moreover,as described above, the state (whether or not running) of asynchronization timer for a specific group (specific synchronizationgroup) is associated with uplink data transmission on the cells of anon-specific group (non-specific synchronization group) other than thespecific group. On the other hand, the synchronization timers TAT arecontrolled independently for the specific group and the non-specificgroup. The specific group and the non-specific group can correspond tothe primary synchronization group and the secondary synchronizationgroup, respectively.

Note that “associate” the synchronization timer for the specific group(primary synchronization group) with uplink data transmission in thespecific group (primary synchronization group) and in the non-specificgroup (secondary synchronization group) is as described already.Independent control of the synchronization timers for the specific group(primary synchronization group) and the non-specific group (secondarysynchronization group) indicates that, for example, thestarting/restarting and stopping of the synchronization timer for eachgroup are performed depending on the reception status of a transmissiontiming adjustment value TA for each group.

Referring to FIG. 13, the radio base station eNB manages cells by usingfour frequency bands f0, f1, f2, and f3, and the radio terminal UEtransmits uplink signals by using, at the same time, all or some of anuplink radio resource on a cell 0 of the frequency band f0 (hereinafter,simply referred to as cell 0), an uplink radio resource on a cell 1 off1 (hereinafter, simply referred to as cell 1), an uplink radio resourceon a cell 2 of f2 (hereinafter, simply referred to as cell 2), and anuplink radio resource on a cell 3 of f3 (hereinafter, simply referred toas cell 3). Here, it is assumed that the cell 0 is a primary cell PCell,and the cells 1 to 3 are secondary cells SCell. Moreover, it is assumedthat the cells 0 and 1 that have the same propagation delays(propagation characteristics) comprise a primary synchronization group,and the cells 2 and 3 that similarly have the same propagation delays(propagation characteristics) comprise a secondary synchronizationgroup.

In third and fourth examples to be described below, an uplink signalfrom the cell 0, which is the primary cell PCell of the primarysynchronization group, or from the cell 1, which is the secondary cellSCell thereof, will simply be referred to as “uplink signal from theprimary synchronization group,” and an uplink signal from the cell 2 orthe cell 3, which are the secondary cells SCell of the secondarysynchronization group, will simply be referred to as “uplink signal fromthe secondary synchronization group.” Moreover, unless otherwiseexplained, uplink signals on the cells 0 and 1 will not bedifferentiated from each other. Similarly, uplink signals on the cells 2and 3 will not be differentiated from each other.

6. Third Example

Next, a description will be given of a method for controllingsynchronization timers used to determine uplink-signal synchronizationat the time of carrier aggregation (CA), by taking a system shown inFIG. 13 as an example. Note that in a third example of the presentinvention, the synchronization timer 1 (107 p) and the synchronizationtimer 2 (107 s) of the radio base station eNB shown in FIG. 7 correspondto a primary synchronization timer TAT-p for a primary synchronizationgroup and to a secondary synchronization timer TAT-s for a secondarysynchronization group, respectively, and the synchronization timer 1(210 p) and the synchronization timer 2 (210 s) of the radio terminal UEshown in FIG. 8 correspond to a primary synchronization timer TAT-p forthe primary synchronization group and to a secondary synchronizationtimer TAT-s for the secondary synchronization group, respectively.

In the present example, the primary synchronization timer for theprimary synchronization group and the secondary synchronization timerfor the secondary synchronization group are controlled independently.Accordingly, even when the primary synchronization timer expires, thesecondary synchronization timer is left continuously running (is notstopped) if the secondary synchronization timer has not expired.However, in this case, even if the secondary synchronization timer isrunning, uplink-signal transmission is not performed in the secondarysynchronization group. Note that even after a synchronization timerexpires, uplink access signals for random access and the like can betransmitted as necessary. Moreover, a reason for giving attention hereto the case where the primary synchronization timer for the primarysynchronization group to which the primary cell belong expires, is thatin LTE, a physical channel (Physical Uplink Control Channel: PUCCH) fortransmitting uplink control signals concerning the Physical Layer andthe MAC Layer (Medium Access Control Layer) can be used only on theprimary cell, and therefore uplink-signal synchronization on the primarycell is most important.

6.1) Synchronization Timer Control

Referring to FIG. 14, at the radio base station eNB, it is determinedbased on, for example, a transmission buffer status report (BufferStatus Report: BSR) whether or not a radio terminal UEx that is acontrol target has (untransmitted) uplink data to transmit (Step 701),and when the radio terminal UEx has uplink data (Step 701; Yes), it isdetermined whether or not the primary synchronization timer (TAT-p) isrunning (Step 702). If the primary synchronization timer (TAT-p) isrunning (Step 702; Yes), it is similarly determined whether or not thesecondary synchronization timer (TAT-s) is running (Step 703).

If the secondary synchronization timer (TAT-s) is also running (Step703; Yes), uplink scheduling is performed for a cell or cells of theprimary synchronization group and/or the secondary synchronization groupdepending on the amount of the uplink data (Step 704), and a schedulinggrant indicating a result of scheduling and (if necessary) atransmission timing adjustment value TA are transmitted (Step 706). Ifthe secondary synchronization timer (TAT-s) is not running (expires)(Step 703; No), uplink scheduling is performed for a cell of the primarysynchronization group (Step 705), and a scheduling grant indicating aresult of scheduling and (if necessary) a transmission timing adjustmentvalue TA are transmitted (Step 706).

On the other hand, if the primary synchronization timer (TAT-p) is notrunning (expires) (Step 702; No), uplink scheduling for the primarysynchronization group is stopped (is not performed thereafter) (Step707). Subsequently, it is determined whether or not the secondarysynchronization timer (TAT-s) is running (Step 708) and, if it isrunning (Step 708; Yes), it is not stopped along with the expiry of theprimary synchronization timer (TAT-p) but is left continuously running(Step 709), while uplink scheduling for the secondary synchronizationgroup is stopped (is not performed thereafter) (Step 710). Then, arequest for uplink resynchronization in the primary synchronizationgroup is made to the radio terminal UEx (Step 711). When uplinkresynchronization in the primary synchronization group is done (Step712; Yes), the primary synchronization timer (TAT-p) is restarted (Step713), and the process moves to Step 703 and similar processing isrepeated thereafter.

Referring to FIG. 15, at the radio terminal UEx, it is determinedwhether or not (untransmitted) uplink data to be transmitted ismaintained (Step 801), and when uplink data is maintained (Step 801;Yes), it is determined whether or not the primary synchronization timer(TAT-p) is running (Step 802).

If the primary synchronization timer (TAT-p) is running (Step 802; Yes),it is similarly determined whether or not the secondary synchronizationtimer (TAT-s) is running (Step 803). If the secondary synchronizationtimer (TAT-s) is also running (Step 803; Yes), a scheduling grantindicating a result of scheduling is received (not shown), and uplinkdata transmission is performed on a cell or cells of the primarysynchronization group and/or the secondary synchronization groupscheduled (Step 804). If the secondary synchronization timer (TAT-s) isnot running (expires) (Step 803; No), uplink data transmission isperformed on a cell of the primary synchronization group scheduled (Step805). The radio terminal UEx makes a buffer status report (BSR) asnecessary along with uplink data transmission (Step 806).

On the other hand, if the primary synchronization timer (TAT-p) is notrunning (expires) (Step 802; No), uplink transmission in the primarysynchronization group (if it is already scheduled) is stopped (is notperformed thereafter) (Step 807). Subsequently, it is determined whetheror not the secondary synchronization timer (TAT-s) is running (Step808), and if it is running (Step 808; Yes), it is not stopped along withthe expiry of the primary synchronization timer (TAT-p) but is leftcontinuously running (Step 809), while uplink transmission in thesecondary synchronization group (if it is already scheduled) is stopped(is not performed thereafter) (Step 810).

Subsequently, processing for uplink resynchronization in the primarysynchronization group is started (Step 811), and when uplinkresynchronization in the primary synchronization group is done (Step812; Yes), the primary synchronization timer (TAT-p) is restarted (Step813), and the process moves to Step 803. In this event, if the secondarysynchronization timer (TAT-s) is still running when uplinkresynchronization in the primary synchronization group is accomplished,uplink transmission can be restarted in the secondary synchronizationgroup without awaiting processing for uplink resynchronization.Thereafter, similar processing is repeated.

6.2) Effects

As described above, according to the third example of the presentinvention, even in a case where there are a plurality of synchronizationgroups each having independent uplink-signal transmission timing, aradio terminal UE can appropriately perform synchronization timercontrol by using synchronization timers corresponding to the respectivesynchronization groups. Moreover, even when resynchronization isaccomplished after the primary synchronization timer (TAT-p) is onceexpired, it is possible to suppress (avoid) a delay until uplinktransmission is restarted on a cell of the secondary synchronizationgroup if the secondary synchronization timer (TAT-s) has been runningsince the expiry of the primary synchronization timer (TAT-p) up untilthe restart thereof.

7. Fourth Example

Next, attention will be given to a method for controlling the secondarysynchronization timer (TAT-s) for the secondary synchronization groupand uplink-signal transmission therein when the primary synchronizationtimer (TAT-p) for the primary synchronization group expires. Insynchronization timer control according to a fourth example of thepresent invention, if the secondary synchronization timer (TAT-s) isstill running even when the primary synchronization timer (TAT-p)expires, uplink data transmission on the cells of the secondarysynchronization group is stopped, but transmission of predeterminedcontrol signals and/or known signals is enabled. Hereinafter, as anexample of the known signals, a sounding reference signal (SoundingReference Signal: SRS) in LTE will be assumed.

Referring to FIG. 16, at the radio terminal UEx, when the primarysynchronization timer (TAT-p) expires (Step 901), uplink transmission onthe cells of the primary synchronization group (if it is alreadyscheduled) is stopped (is not performed thereafter) (Step 902).

Subsequently, it is determined whether or not the secondarysynchronization timer (TAT-s) is running (Step 903). When the secondarysynchronization timer (TAT-s) is not running either (expires) (Step 903;No), uplink transmission on the cells of the secondary synchronizationgroup (if it is already scheduled) is stopped (is not performedthereafter) (Step 904).

On the other hand, if the secondary synchronization timer (TAT-s) isrunning (Step 903; Yes), uplink data transmission on the cells of thesecondary synchronization group (if it is already scheduled) is stopped(is not performed thereafter) (Step 905). However, the secondarysynchronization timer (TAT-s) is left continuously running (Step 906).Then, while the secondary synchronization timer (TAT-s) is running,transmission of uplink sounding reference signals (SRS) (if it isalready scheduled) is continued on the cells of the secondarysynchronization group (Step 907). Then, the process goes back to Step903 and the above-described processing is repeated.

As described above, according to the fourth example of the presentinvention, even when uplink synchronization is lost in the primarysynchronization group, since transmission of uplink sounding referencesignals (SRS) is continued as long as uplink synchronization in thesecondary synchronization group is maintained, the radio base stationeNB can check the quality of uplink communication and confirm uplinksynchronization on the cells of the secondary synchronization group.Thereby, it is also possible to appropriately perform scheduling foruplink data transmission on a cell of the secondary synchronizationgroup after uplink resynchronization in the primary synchronizationgroup is accomplished. Furthermore, the radio base station eNB can alsoperform checking as to whether or not the radio terminal UE is stillpresent in a cell covered by itself, and the like.

9. Other Examples

In the hitherto-described embodiment and examples, a description is madeon the premise that the physical channel (PUCCH) transmitting (some of)uplink control signals concerning the Physical Layer and the MAC Layercan be used only on a primary cell. However, the present invention isnot limited to this, but can also be applied in a case where thephysical channel (PUCCH) transmitting such uplink control signals isused on a secondary cell. For example, in a case where the physicalchannel (PUCCH) can be used on at least one cell of each synchronizationgroup, it is also possible to allow transmission of uplink signals,irrespective of their types, to be performed or continued in a certainsynchronization group as long as uplink-signal synchronization ismaintained on the cell of this synchronization group, regardless ofuplink-signal synchronization on the primary cell.

Moreover, conceivable methods for configuring a synchronization group(TA Group) are as follows.

First, for carrier aggregation (CA) in LTE, serving cell indexes(ServCelllndex) are defined to correspond to individual cells. Forexample, a serving cell index “0” is assigned to a primary cell (PCell),and serving cell indexes “1 to 7” are respectively assigned to secondarycells (SCell). Further, secondary cell indexes (SCellIndex) are alsodefined. Secondary indexes “1 to 7” correspond to the serving cellindexes “1 to 7” respectively. Since a primary cell always has theserving cell index “0,” a radio base station (eNB) does not particularlynotify a radio terminal (UE) of information about the serving cell indexof the primary cell. However, each secondary cell index is notified froma radio base station (eNB) to a radio terminal (UE) when a secondarycell is configured (configure SCell).

Here, for a method for configuring a synchronization group (TA Group),when secondary cells are configured, that is, when secondary cellindexes are notified, a synchronization group index (number) (TA GroupIndex or TA Group ID) may be notified from a radio base station (eNB) toa radio terminal (UE), or information about a synchronization groupindex and corresponding cells or frequencies may be broadcast orindividually notified to radio terminals (UEs) in the cells. Note that asynchronization group index may be notified only when configuration ofan uplink radio resource (component carrier CC) corresponding to asecondary cell of interest is involved. Moreover, it is conceivable thata synchronization group index of a primary synchronization group (PCellTA Group) including a primary cell is set for “0” and synchronizationgroup indexes of secondary synchronization groups (SCell TA Groups) areset for consecutive numbers starting from “1,” but the present inventionis not limited to this.

Furthermore, in the hitherto-discussed examples, a description has beengiven with 3GPP LTE in mind for the radio communication systems.However, the targets of the present invention are not limited to thesebut can be applied to GSM (Global System for Mobile communications),UMTS (Universal Mobile Telecommunications System), WiMAX (Worldwideinteroperability for Microwave Access), and the like.

INDUSTRIAL APPLICABILITY

The present invention is applicable to transmission timing control inradio communication systems such 3GPP LTE, GSM, UMTS, and the like.

REFERENCE SIGNS LIST

-   10 Radio base station-   101 Reception section-   102 Demodulation section-   103 Upper layer-   104 Timing control unit (UEx)-   105 Transmission signal generation section-   106 Transmission section-   107 p Synchronization timer (TAT1)-   107 s Synchronization timer (TAT2)-   108 TA1 calculation and retention section-   109 TA2 calculation and retention section-   20 Radio terminal-   201 Reception section-   202 Demodulation section-   203 Upper layer-   204 Timing control unit-   205 Transmission signal generation section-   206 Transmission section-   208 TA1 management unit-   209 TA2 management unit-   210 Synchronization timer (TAT1)-   211 Synchronization timer (TAT2)

1-27. (canceled)
 28. A radio terminal comprising: at least one processorconfigured to aggregate a first cell group with a second cell group,wherein the first cell group includes a first cell on which a firstPhysical Uplink Control Channel (PUCCH) is transmitted and the secondcell group includes a second cell on which a second PUCCH istransmitted; a first timer associated with the first cell group, whereinthe first timer is used to control whether uplink transmission of theradio terminal in at least one of serving cells of the first cell groupis synchronized; and a second timer associated with the second cellgroup, wherein the second timer is used to control whether uplinktransmission of the radio terminal in at least one of serving cells ofthe second cell group is synchronized, wherein the radio terminal doesnot perform the uplink transmission except for a random access preambletransmission by the radio terminal in at least one of serving cells ofthe first cell group when the first timer expires, and the radioterminal does not perform the uplink transmission except for a randomaccess preamble transmission by the radio terminal in at least one ofserving cells of the second cell group when the first timer expires. 29.The radio terminal according to claim 28, wherein expiry of the firsttimer associated with the first cell group does not affect an operationfor the second timer associated with the second cell group.
 30. Theradio terminal according to claim 29, wherein the radio terminal furthercomprises: a receiver configured to receive at least one of a firsttiming advance command and a second timing advance command, wherein theat least one processor is further configured to: start or restart thefirst timer when the first timing advance command is received, and startor restart the second timer when the second timing advance command isreceived.
 31. A control method in a radio terminal configured toaggregate a first cell group with a second cell group, wherein the firstcell group includes a first cell on which a first Physical UplinkControl Channel (PUCCH) is transmitted and the second cell groupincludes a second cell on which a second PUCCH is transmitted, thecontrol method comprising: controlling whether uplink transmission ofthe radio terminal in at least one of serving cells of the first cellgroup is synchronized, by using a first timer associated with the firstcell group; controlling whether uplink transmission of the radioterminal in at least one of serving cells of the second cell group issynchronized, by using a second timer associated with the second cellgroup, wherein the radio terminal does not perform the uplinktransmission except for a random access preamble transmission by theradio terminal in at least one of serving cells of the first cell groupwhen the first timer expires, and the radio terminal does not performthe uplink transmission except for a random access preamble transmissionby the radio terminal in at least one of serving cells of the secondcell group when the first timer expires.
 32. The method according toclaim 31, wherein expiry of the first timer associated with the firstcell group does not affect an operation for the second timer associatedwith the second cell group.
 33. The method according to claim 31, themethod further comprises: receiving at least one of a first timingadvance command and a second timing advance command; starting orrestarting the first timer when the first timing advance command isreceived; and starting or restarting the second timer when the secondtiming advance command is received.